This invention relates to a development apparatus for developing electrostatic images upon a moving image-bearing surface. Flow baffle means are included for regulating the flow of developer to the development zone. The flow baffle means comprise stationary magnetic brushes.
In prior art magnetic brush development apparatuses, a problem has occurred with respect to the copy quality output of the electrostatic reproducing machines in which they are employed. In some machines a high background region is formed on each of the end portions of the copy sheet due to higher flow rates of developer at the end portions of a magnetic brush development means. The higher flow rates at the ends of the magnetic brush development means are due at least in part to the presence of fringe fields at the ends of the brush forming magnets within the development means which attract an increased amount of developer to the ends of the magnetic roll. The increased flow of developer coupled with fringe fields at the ends of the magnetic brush roll results in a higher density of developer at the ends of the roll and, therefore, a consequent increase in the background level on the end portions of the copy sheet.
In U.S. Pat. Nos. 3,648,656, granted Mar., 1972, and 3,754,526, granted Aug., 1973, there are disclosed magnetic brush evelopment apparatuses wherein magnetic field generating means are employed to prevent the developer from being picked up by the end portions of the magnetic brush rolls. These patents use magnetic fields to control the flow of developer, but do not employ stationary magnetic brushes in accordance with this invention to mechanically control the flow of developer.
The use of a magnetic means interposed between a bearing and a flow of magnetic particles is described in U.S. Pat. No. 2,996,162, granted August, 1961, and in U.S. application Ser. No. 266,905, filed June 28, 1972. In these devices a magnetic flux field produced by the magnetic means entraps and aligns the magnetic granules into a brush which acts to seal the bearings from the flow of magnetic particles. The patent and application do not use the magnetic seal brushes as flow baffles to regulate the flow of developer to the development zone of a development apparatus.